This invention relates to optical devices for reading a coded record on a substrate, and is more particularly directed to an optical scanning device for reading the coded records on a record member, such as a badge, card or ticket.
Bar coded badges have become increasingly popular in government and in industry, both for security access systems and for time and attendance purposes. In reading bar-coded identification badges, the bar coded area on the badge is positioned to move past the bar code reader or scanner in the badge reader. Typically, the badge is made up of a blank card or substrate, and a bar code symbol made up of a row of alternating dark and light stripes, is positioned a short distance from one edge of the card. Then other items, such as a photograph of the employee and a frame, can be placed on the card. Thereafter it is overlaid with a durable clear plastic laminate.
It is usually the case that the parts of the badge, particularly at the lateral edges of the badge, do not have a uniform thickness. Consequently, the overlay or laminate can be somewhat uneven or wavy at lead-in areas at the left and right ends of the bar code symbol. This unevenness can result in undesirable specular reflection into the scanner.
All known badge readers, employing LEDs, use either a single illuminating LED, two LEDs oriented in the horizontal plane, or four LEDs in crossed planes.
A single LED oriented in the horizontal plane, i.e., to the left or right of the optic axis and on the optical center line, can produce specular reflection at one end of the badge. A pair of LEDs oriented horizontally but on opposite sides of the optic axis can produce specular reflection at both ends of the badge, but the amount of desirable diffuse reflection from the bar code symbol will be twice that of the single LED arrangement.
An arrangement employing four LEDs, one to the right and one to the left of the optic axis, and two disposed respectively above and below the optical center line, will provide a signal four times the strength of a single LED arrangement. However, this arrangement is still susceptible to specular reflections at the lead-in areas at both ends, and is more expensive than a two LED arrangement in terms of component and manufacturing costs.
A single LED arrangement, with an LED situated in a plane perpendicular to the direction of badge travel, will be relatively insensitive to specular reflection caused by waviness in the laminate at the leading and trailing ends of the bar code symbol. However, the single LED arrangement will not have the high signal level of the multiple LED arrangements, and will not be immune to specular reflection caused by waviness occurring along a plane transverse to the direction of badge travel.